Numerous analytical methods have been developed for determining the presence or absence and/or quantifying the amount of various analytes in tissues and fluids of organisms, such as blood, urine, fecal material, or tissue biopsy. Lateral flow chromatography is, perhaps, one of the more common of these analytical methods.
Lateral flow chromatography assays and devices are well known to those of skill in the art (see, e.g., U.S. Pat. Nos. 5,569,608, 5,120,643, 5,656,503, 4,855,240, and 5,591,645, British Patent GB 2204398A, and European patent EP 0323605 B1) and such assays are commercially available on a retail or OEM basis for numerous analytes.
Lateral flow immunoassays typically involve the application of a liquid test sample suspected of containing an analyte to be detected to an application zone of a lateral flow (immunochromatographic) test strip. The strip is comprised of a matrix material (e.g., paper, nitrocellulose, etc., see, e.g., U.S. Pat. No. 5,569,608) through which the test fluid and analyte suspended or dissolved therein can flow by capillarity from the application zone to a detection zone where a visible signal, or absence of such, reveals the presence or absence of the analyte.
Typically, the strip will include means for immunospecifically binding the analyte to be detected with its specific binding partner (e.g., where the analyte is an antigen, the binding partner is an antibody or antibody fragment, and vice versa) which bears a detectable label. In one such scheme, as disclosed in U.S. Pat. No. 4,446,232, the strip contains an enzyme labeled, mobile binding partner for the analyte which is in a zone downstream from the sample application zone. If the analyte is present in the test sample, it will combine with its labeled binding partner to form a complex which will flow along the strip to a zone which contains a substrate for the enzyme label capable of providing a signal (e.g., a colored response) in the presence of the enzyme label.
The strip typically contains a zone in which an analyte is immobilized, so that the labeled binding partner which does not combine with analyte, due to absence of analyte in the sample, will be captured and thereby inhibited from reaching a zone downstream. There have been published various modifications of this technique, many of which involve some competitive specific binding system in which the presence or absence of analyte in the test sample is determined by the detection or lack thereof of labeled binding partner in a particular device zone. In U.S. Pat. No. 4,868,108 there is disclosed a similar scheme with the addition of an immobilized capture reagent for the enzyme labeled binding partner in a particular zone to concentrate the enzyme label and enhance its ability to react with the enzyme substrate and thereby render the assay more sensitive.
Not all of the schemes for immunochromatography rely on an enzyme labeled binding partner/enzyme substrate as providing the signal for detection of the analyte. In U.S. Pat. No. 4,806,311 there is disclosed a multizone test device for the specific binding assay determination of an analyte and an immobilized binding partner together with a downstream zone for receiving labeled reagent which migrates thereto from an upstream zone. The downstream zone contains an immobilized form of a binding substance for the labeled reagent. The labeled reagent bears a detectable chemical group having a detectable physical property such as a luminescent group (e.g. a fluorescent or phosphorescent moiety), radioisotopes and electroactive moieties. U.S. Pat. No. 4,313,734 describes the use of gold sols as labels for antibodies which are detectable.
Many lateral flow immunochromatography systems utilize particulate (microparticle) markers (e.g., gelatin, dyed latex, or colloidal gold) which are labeled with a binding partner (e.g., antibody or antigen) that binds the analyte of interest.
The microparticles or other detectable moieties attached to an analyte binding moiety (e.g., an antibody or antigen) are dried onto (or otherwise localized in) either a lateral flow chromatographic strip or onto a sample application pad (typically glass fiber) which in turn is affixed to one end of a strip of chromatographic medium such as nitrocellulose. Another material binding to the analyte of interest is affixed to the chromatographic medium at or near the end opposite to the end having the application pad.
The liquid sample to be analyzed is placed on the pad, causing the suspension of the microparticles into the liquid and allowing any analyte in the liquid sample to bind to the analyte-binding material attached to the microparticles. The liquid sample leaves the application pad by diffusion and capillary action and begins to migrate along the nitrocellulose strip carrying the microparticles down the strip along with the liquid. When the liquid containing the suspended microparticles arrives at the region of the chromatographic strip bearing the second binding material, the analyte (if present in the original sample) will form a bridge between the analyte-binding material on the microparticles and the analyte-binding material affixed to the strip, resulting in the immobilization of the microparticles at that point on the strip where the analyte-binding material is affixed. This immobilization of the microparticles results in a visible signal (e.g., a colored band or dot) at this point on the strip. If the analyte is not present in the sample, the microparticles will continue past this location on the chromatographic strip and a visible signal will not be produced.
It will be appreciated that other labels (e.g., fluorescent labels) besides microparticles can be utilized. In addition, a single chromatography strip can contain reagents to detect or quantify a number of different analytes.
It will also be appreciated that the lateral flow strip can use an analyte detection that does not involve an antibody-antigen recognition system. Thus, for example, the strip can be impregnated in a detection zone with a chemical that reacts with the analyte itself to produce a signal.
Existing lateral flow chromatographic devices often fail to provide sufficient stability to the components of the test device, such as peptides, proteins (e.g. antibodies and fragments thereof), ligands, and nucleic acids. In addition, currently existing devices do not provide adequate control over the time in which the analyte is allowed to bind to detectable reagents of the assay. By providing a novel bulking material, the present invention solves these and other needs.